This invention relates to a three-way electromagnetic valve suitable for use in a system for controlling a high pressure fluid, for example, a diesel fuel injection system.
In a diesel engine fuel injection system such as the one disclosed in Japanese Patent Laid-Open No. 59-165858, a three-way electromagnetic valve is used to control the injection timing and the injection rate. This three-way electromagnetic valve operates in such a manner that a fuel supplied at a high pressure from a pressure fuel feed pump is led from a fuel passage to a supply port and is supplied to a chamber formed in a moving piston and to a control port via an annular recess and a plurality of fuel passages formed in the moving piston and communicating with the recess.
A high pressure is applied to the valve body at the annular recess outward in the radial direction by the effect of the high pressure fuel led to the recess, thereby increasing the clearance of the slide section formed between the slide bore and the moving piston. The high pressure fuel therefore leaks and enters the increased clearance and presses not only the recess 8 but also the whole of the bore wall, and further increases the clearances of upper and lower slide sections defined above and below the annular recess, resulting in an increase in the leakage of the high pressure fuel.
A solenoid, the valve body and a control chamber are integrally fixed by fastening to construct the three-way valve while maintaining the desired pressure at which contact surfaces of the valve body and the control chamber are pressed against each other. Since in this construction a spacer in the form of a ring is interposed between the solenoid and the valve body, the fastening force acts toward the outer periphery of the valve body at the upper surface thereof and causes the bore edge of the slide bore to be deformed outward. The clearances of the slide sections between the slide bore and the moving piston are thereby increased toward the bore edge, resulting in a further increase in the leakage of the high pressure fuel.
As described above, if the clearances of the slide sections are increased, the leakage of the high pressure liquid through these clearances becomes large. This three-way electromagnetic valve therefore entails the problem of loss of the driving torque of the pressure fuel feed pump, the problem of a reduction in the fuel injection pressure, and so on.